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RFC 1771

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Network Working Group
Request for Comments: 1771
Obsoletes: 1654
Category: Standards Track

Y. Rekhter
T.J. Watson Research Center, IBM Corp.
T. Li
cisco Systems
Editors
March 1995

### A Border Gateway Protocol 4 (BGP-4)

### Status of this Memo

This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.

### Abstract

This document, together with its companion document, "Application of the Border Gateway Protocol in the Internet", define an inter- autonomous system routing protocol for the Internet.

### Table of Contents

1. Acknowledgements
2. Introduction
3. Summary of Operation

3.1 Routes: Advertisement and Storage
3.2 Routing Information Bases

4. Message Formats

4.1 Message Header Format
4.2 OPEN Message Format
4.3 UPDATE Message Format
4.4 KEEPALIVE Message Format
4.5 NOTIFICATION Message Format

5. Path Attributes

5.1 Path Attribute Usage

5.1.1 ORIGIN
5.1.2 AS_PATH
5.1.3 NEXT_HOP
5.1.4 MULTI_EXIT_DISC
5.1.5 LOCAL_PREF
5.1.6 ATOMIC_AGGREGATE
5.1.7 AGGREGATOR

6. BGP Error Handling.

6.1 Message Header error handling.
6.2 OPEN message error handling.
6.3 UPDATE message error handling.
6.4 NOTIFICATION message error handling.
6.5 Hold Timer Expired error handling.
6.6 Finite State Machine error handling.
6.7 Cease.
6.8 Connection collision detection.

7. BGP Version Negotiation.
8. BGP Finite State machine.
9. UPDATE Message Handling

9.1 Decision Process

9.1.1 Phase 1: Calculation of Degree of Preference
9.1.2 Phase 2: Route Selection

9.1.2.1 Breaking Ties (Phase 2)

9.1.3 Phase 3: Route Dissemination
9.1.4 Overlapping Routes

9.2 Update-Send Process

9.2.1 Internal Updates

9.2.1.1 Breaking Ties (Internal Updates)

9.2.2 External Updates
9.2.3 Controlling Routing Traffic Overhead

9.2.3.1 Frequency of Route Advertisement
9.2.3.2 Frequency of Route Origination
9.2.3.3 Jitter

9.2.4 Efficient Organization of Routing Information

9.2.4.1 Information Reduction
9.2.4.2 Aggregating Routing Information

9.3 Route Selection Criteria
9.4 Originating BGP routes

Appendix 1. BGP FSM State Transitions and Actions.
Appendix 2. Comparison with RFC1267
Appendix 3. Comparison with RFC 1163
Appendix 4. Comparison with RFC 1105
Appendix 5. TCP options that may be used with BGP
Appendix 6. Implementation Recommendations

6.1 Multiple Networks Per Message
6.2 Processing Messages on a Stream Protocol
6.3 Reducing route flapping
6.4 BGP Timers
6.5 Path attribute ordering
6.6 AS_SET sorting
6.7 Control over version negotiation
6.8 Complex AS_PATH aggregation

References
Security Considerations
Editor's Addresses

Original text document

Next: 1. Acknowledgements

Connected: An Internet Encyclopedia
RFC 1771